Dark energy is driving the accelerating expansion of the universe. No one knows what it is.

Today, a giant radio telescope in Western Canada is being turned on to begin its mission tracking the expanding growth of the universe. Scientists hope to find out more about the mysterious force behind this accelerating expansion—what they call dark energy. This makes up the majority of the universe, but we have no idea what it is.

The $16-million Canadian Hydrogen Intensity Mapping Experiment, CHIME for short, is made of what looks like four 100-metre-long snowboard halfpipes stuck next to each other, and uses radio signals to detect hydrogen intensity. It's a way to measure how much of the universe has expanded and how quickly, in the slice of space that can be viewed from Canada. That data will be collected and processed into a 3D map of the sky. The project is a collaboration between several universities—the University of British Columbia, University of Toronto, and McGill—and the National Research Council of Canada.

I reached principal investigator Mark Halpern, astronomy professor at UBC, over the phone at the Dominion Radio Astrophysical Observatory in the British Columbia interior near Penticton, the site of the project. He had to take the call from a closed-off metal room to avoid producing too much radio interference, which could harm the integrity of their results. As is common with radio telescopes, no cellphones are allowed on the premises.

The telescope is near Penticton, BC. Image: CHIME

Halpern said that, by mapping the spread of hydrogen in space, he and his team can identify existing galaxies to see if they've expanding outwards, and can tell how far away the light from these objects is from Earth, which is a way to measure distance (a process called redshift).

"If we know those two things—expansion and distance—then we can put together an expansion history," he said.

The universe hasn't stopped expanding since the Big Bang 13.8 billion years ago. In fact, the expansion is now happening at an accelerated rate, pushed by an enigmatic repulsive force called dark energy. Halpern said that there's twice as much dark energy as everything else in the entire universe combined, yet what it actually is remains a total mystery. "The plain truth is," he said, "we don't have a clue."

Over the course of the next five years, this radio telescope will create the biggest 3D map ever made—and the team will use mainly cheap, commercially available technologies to do it, according to Halpern. The radio signals are sent out using about a thousand cellphone transistors, and the 3D maps are being processed in part by computers with video-game-grade graphics cards.

"I think we're lucky to live in a time where this technology is readily available," partly because of a booming consumer market for these products, Halpern said. "If we tried to do this a decade ago, every little bit of it would have been a custom-made part and unbelievably expensive."

Instead of being designed like a regular radio telescope—shaped like a round satellite dish—CHIME was made into the halfpipe design to be able to map out and observe several lines in the sky, as opposed to specific dots that a typical telescope could focus on.

Though the team won't have any results about the expansion history and dark energy for a few years, CHIME is also testing more short-term experiments, like measure the signals of all known pulsars, as well as identify mysterious fast radio bursts.